The present invention relates to an automatic brightness correction apparatus for automatically corrects the brightness property of the image display device.
Conventionally an automatic brightness correction apparatus was mainly used for balancing R, G and B colors, i.e., three primary colorsxe2x80x94red (R), green (G), blue (B). Accordingly, it had a system for adjusting the gain by detecting the brightness levels at the time that the black level images for the R, G and B color signals have been displayed, respectively.
An example of the automatic brightness correction apparatus for correcting the brightness property of image display devices is discussed in the xe2x80x9cNHK Television Technical Textbook, Vol. 1, 7.3.1(2), Chapter; Automatic White Balance Circuit,xe2x80x9d published by NHK (Nihon House Kyoukai; Japanese Broadcast Association).
In such a conventional automatic brightness correction apparatus, since it correct by detecting only the lowest level (black level) and the highest level (white level) of the video signal, it could not correct brightness property at the intermediate level in detail.
Here, in the case of general color CRT (cathode-ray tube) three electron guns for displaying respective images of the R, G and B color signals are mounted in one CRT. While the efficiency of each electron gun is deteriorated with the passage of time. Further, the degrees of the efficiency deterioration vary among the electron guns. Accordingly, while the conventional R, G and B color balance correction system is able to ensure the balances at the black level and the white level, it fails to ensure a color balance at an intermediate level.
In the general NTSC TV, since it has a lower resolution, and it displays mainly the moving image, an unbalance of the R, G and B colors at the intermediate level is unobtrusive for viewers and thus not become controversial. However, in the high definition monitor such as for the medical treatment, since it displays the high definition still image a color unbalance of the R, G and B electric guns will become controversial.
Further, in different from the general color CRT a single electron gun type CRT is free from such an R, G and B color unbalance problem. However, the brightness property at an intermediate level is apt to deteriorate from its initial property with the passage of time. Such a case will be the problem in the monitor requiring high-performance brightness property at the intermediate level such as the high definition monitor such as for the medical treatment.
Furthermore, in the multi-screen display device which displays fractions of one image on a number of CRTs in a multi-CRT display device, the images will be hard to see when there is an unbalance between brightness of adjacent CRTs. So, in the conventional system the brightness properties at the black level and the white level are kept equal for every CRT. However, since the brightness properties of CRTs at the intermediate levels may gradually account for differences with the passage of time the image and thus becomes hard to be viewed for viewers.
In the conventional automatic brightness correction apparatus mentioned above, since it detects and corrects the brightness at only the lowest level (black level) and the highest level (white level) of the image signal, it can not correct the brightness at the intermediate level, so that it generates the image deterioration such as the unbalance of the R, G and B colors at the intermediate level because of the deterioration of the efficiency of electron guns with the passage of time.
It is, therefore, an object of the present invention is to provide an automatic brightness correction apparatus which performs the highly accurate automatic brightness correction for the intermediate level image signals.
In order to achieve the above object, an automatic brightness correction apparatus for automatically correcting the brightness property of the image display device according to one aspect of the present invention is configured to insert a test pulse at a predetermined level within a level range including an intermediate level to the video signal and displays the image of the test pulse on the video image display device, detect a deviation of the brightness of the image of the test pulse displayed on the video image display device from a benchmark, and correct the level of the video signal based on the detected deviation.
Additional objects and advantages of the present invention will be apparent to persons skilled in the art from a study of the following description and the accompanying drawings, which are hereby incorporated in and constitute a part of this specification.